A wire, shown in Figure P17.48, moves downward perpendicular to a magnetic field.
(a) In what direction will the electrons in the wire move?
(b) After the electrons are forced in one direction, leaving positive charges behind, an $\vec{E}$ field and potential difference $\Delta V$ develop from one end of the wire to the other. The electrons no longer move, since the electric and magnetic forces exerted on them
balance. Show that this happens when the potential difference
from one end of the wire to the other is $\Delta V=v L B$ , where $v$ is
the speed of the wire, $L$ is its length, and $B$ is the magnitude of
the magnetic field. Describe two real-world situations where
this phenomenon might occur.